Performance Evaluation Of Air Flotation Equipment And Research On Decontamination Mechanism

Aiming at the treatment of low temperature,low turbidity and high algae water,dissolved air flotation(DAF)process is gradually applied to water supply treatment.As a solid-liquid separation technology,the DAF process has advantages in removing light colloidal particles in water.DAF equipment is the key to the dissolved air system.The performance of the equipment directly determines the adhesion efficiency and decontamination efficiency of the DAF process.At present,DAF equipment has problems such as uneven parameters,unstable performance,and lack of evaluation technology.In order to explore the factors affecting DAF equipment,researched on the performance and decontamination effect of DAF equipment that conduct laboratory,pilot and production evaluation,optimize process parameters,and investigate the relationship between air flotation equipment performance parameters and decontamination efficiency,and studied the adhesion of microbubbles and flocs and the removal mechanism of air-entrained flocs,to provide technical support for the evaluation of the operation of air flotation equipment in water plants.By optimizing the performance parameters of the air flotation equipment,and researching the equipment performance and decontamination efficiency of different air flotation equipment under the conditions of small-scale and pilot-scale tests,it is measured that the dissolved air efficiency of the two equipment is about 55%.The average particle size of the bubbles is less than 30?m,and the bubble stabilization time is more than 4min under certain pressure conditions,and the dissolved oxygen content in the water increases significantly after air floatation.The research results show that the equipment performance affects the decontamination efficiency,and the size of the microbubbles is the main factor affecting the decontamination efficiency of the air flotation process.The experiment shows that the particle size of the microbubbles is related to the dissolved gas pressure and the dissolved gas efficiency,the higher the efficiency of dissolved gas,the greater the pressure of dissolved gas,the smaller the particle size of the generated microbubbles,and the greater the density of bubbles.The change rule of decontamination efficiency is consistent with the change rule of equipment performance parameters,and both reach the optimal working condition when the dissolved gas pressure is0.4MPa.In the pilot experiments,the removal rates of conventional air flotation technology for turbidity,chlorophyll a,TOC,UV₂₅₄ are 95.76%,96.41%,34.21%,65.96%,respectively.The pollutant removal rate of Posi-DAF is higher than that of ordinary air flotation.In the pilot test,the removal rates of DAF for turbidity,chlorophyll a,TOC,UV₂₅₄ and COD_Mnare 56.49%,50.23%,23.73%,28.75%,23.98%,respectively,the effect is stable during continuous operation.Evaluated and researched the air flotation equipment of Yuqing Water Plant,Nankang Water Plant,Bailang River Water Plant,and Meicun Water Plant.The overall performance of the air flotation equipment was able to meet the normal process operation,and the dissolved air efficiency of the air flotation equipment of each water plant was 58.4%?78.7%;The bubble size is less than 30?m,and as the rising height increases,the average particle size of the microbubbles increases,and the number density of the microbubbles gradually decreases;the bubble stabilization time is basically stable above 4min.After applying the air flotation process in various water plants,the effluent quality has been greatly improved.The higher electrical energy and chemical consumption generated by the operation of the DAF process can offset each other through the reduction of other indicators,which improves the quality of the effluent.Therefore,the total energy consumption increase after the air flotation process is relatively small,which also provides an economic basis for the promotion of the air flotation process.The research on the mechanism of the removal characteristics of pollutants by the air flotation process found that the removal of algae and organic matter by microbubbles is mainly for high-molecular-weight substances with strong hydrophobicity.The removal effect mainly depends on the hydrophobic interaction between microbubbles and algae and organic matter.The removal effect of modified air flotation is significantly improved,and macromolecular substances such as humic acid are converted into humic acid degradation products,indicating that the hydroxyl radicals generated by the rupture of microbubbles have redox effects.The long-chain structure of the surface modifier molecules helps to form a larger adhesion network,which increases the scanning area and attachment points of the microbubbles,and the modifier will be taken away in the scun with microbubbles.It provides a bridging effect for the adhesion of microbubbles and floc particles,and strengthens the mechanism of conventional air flotation.The separation of the air-entrained flocs depends on the relationship between the surface load and the rising flow rate.The surface load should be lower than the minimum air-entrained flocs'rising speed to ensure a good water output effect.